/* ==========================================
 * JGraphT : a free Java graph-theory library
 * ==========================================
 *
 * Project Info:  http://jgrapht.sourceforge.net/
 * Project Creator:  Barak Naveh (http://sourceforge.net/users/barak_naveh)
 *
 * (C) Copyright 2003-2006, by Barak Naveh and Contributors.
 *
 * This library is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or
 * (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this library; if not, write to the Free Software Foundation,
 * Inc.,
 * 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
 */
/* -------------------------
 * AbstractPathElement.java
 * -------------------------
 * (C) Copyright 2006-2006, by France Telecom
 *
 * Original Author:  Guillaume Boulmier and Contributors.
 * Contributor(s):   John V. Sichi
 *
 * $Id: AbstractPathElement.java,v 1.2 2007/05/22 15:52:53 kjellw Exp $
 *
 * Changes
 * -------
 * 05-Jan-2006 : Initial revision (GB);
 * 14-Jan-2006 : Added support for generics (JVS);
 *
 */
package org.jgrapht.alg;

import java.util.*;

import org.jgrapht.*;

/**
 * A new path is created from a path concatenated to an edge. It's like a linked
 * list.<br>
 * The empty path is composed only of one vertex.<br>
 * In this case the path has no previous path element.<br> .
 * 
 * <p>
 * NOTE jvs 14-Jan-2006: This is currently an internal data structure for use in
 * algorithms. If we want to promote it to public, we should first clean it up
 * and move it to the parent package, making a Path a first-class concept.
 */
abstract class AbstractPathElement<V, E> {
	// ~ Instance fields
	// --------------------------------------------------------

	/**
	 * Number of hops of the path.
	 */
	protected int nHops;

	/**
	 * Edge reaching the target vertex of the path.
	 */
	protected E prevEdge;

	/**
	 * Previous path element.
	 */
	protected AbstractPathElement<V, E> prevPathElement;

	/**
	 * Target vertex.
	 */
	private V vertex;

	// ~ Constructors
	// -----------------------------------------------------------

	/**
	 * Creates a path element by concatenation of an edge to a path element.
	 * 
	 * @param pathElement
	 * @param edge
	 *            edge reaching the end vertex of the path element created.
	 */
	protected AbstractPathElement(Graph<V, E> graph,
			AbstractPathElement<V, E> pathElement, E edge) {
		this.vertex = Graphs.getOppositeVertex(graph, edge, pathElement
				.getVertex());
		this.prevEdge = edge;
		this.prevPathElement = pathElement;

		this.nHops = pathElement.getHopCount() + 1;
	}

	/**
	 * Copy constructor.
	 * 
	 * @param original
	 *            source to copy from
	 */
	protected AbstractPathElement(AbstractPathElement<V, E> original) {
		this.nHops = original.nHops;
		this.prevEdge = original.prevEdge;
		this.prevPathElement = original.prevPathElement;
		this.vertex = original.vertex;
	}

	/**
	 * Creates an empty path element.
	 * 
	 * @param vertex
	 *            end vertex of the path element.
	 */
	protected AbstractPathElement(V vertex) {
		this.vertex = vertex;
		this.prevEdge = null;
		this.prevPathElement = null;

		this.nHops = 0;
	}

	// ~ Methods
	// ----------------------------------------------------------------

	/**
	 * Returns the path as a list of edges.
	 * 
	 * @return list of <code>Edge</code>.
	 */
	public List<E> createEdgeListPath() {
		List<E> path = new ArrayList<E>();
		AbstractPathElement<V, E> pathElement = this;

		// while start vertex is not reached.
		while (pathElement.getPrevEdge() != null) {
			path.add(pathElement.getPrevEdge());

			pathElement = pathElement.getPrevPathElement();
		}

		Collections.reverse(path);

		return path;
	}

	/**
	 * Returns the number of hops (or number of edges) of the path.
	 * 
	 * @return .
	 */
	public int getHopCount() {
		return this.nHops;
	}

	/**
	 * Returns the edge reaching the target vertex of the path.
	 * 
	 * @return <code>null</code> if the path is empty.
	 */
	public E getPrevEdge() {
		return this.prevEdge;
	}

	/**
	 * Returns the previous path element.
	 * 
	 * @return <code>null</code> is the path is empty.
	 */
	public AbstractPathElement<V, E> getPrevPathElement() {
		return this.prevPathElement;
	}

	/**
	 * Returns the target vertex of the path.
	 * 
	 * @return .
	 */
	public V getVertex() {
		return this.vertex;
	}
}

// End AbstractPathElement.java
